Cold-water immersion and heart rhythm in middle-aged recreational swimmers

A self-controlled field study tracked 20 middle-aged recreational athletes with continuous ECG monitoring across 64 cold-water immersion sessions at a large open-water swimming event. Arrhythmic events during immersion were rare and, when they did occur, were brief and benign, with no statistically significant difference in event rates between immersion and non-immersion periods.

What the study found

The study found no meaningful elevation in arrhythmic burden specifically during cold-water immersion compared with ordinary daily activity. Only one arrhythmic episode — a brief, self-terminating run of rapid atrial beats — occurred across all 64 recorded immersion sessions, and no sustained or clinically significant rhythm disturbances were detected at any point.

Heart rate did rise substantially during immersion, climbing on average by roughly 40 beats per minute, a 43% increase over resting values. Despite this cardiovascular stress, the rate of arrhythmic events per hour during immersion (0.12) was not statistically different from the rate during non-immersion periods (0.037), meaning the difference observed could plausibly reflect chance.

Over the full 10-day monitoring window, 85% of participants experienced at least one brief arrhythmic episode, but these were distributed across the monitoring period rather than concentrated around immersion sessions. The authors characterize the overall arrhythmic burden associated with cold-water immersion in this context as low.

It is worth noting that the sample skewed toward elevated cardiovascular risk: more than a third of participants carried a high 10-year cardiovascular risk score, making the absence of serious events somewhat notable, though the small sample limits how far that observation can be generalized.

Limits worth knowing

The sample was very small (n = 20) and drawn from a self-selected group of experienced recreational cold-water swimmers who voluntarily attend a competitive open-water event, which likely excludes individuals with symptomatic cardiac conditions or low cold-water tolerance. The monitoring device used a single lead, which is less sensitive than clinical multi-lead ECG for detecting certain arrhythmia types. The 10-day window, while longer than most acute studies, cannot speak to cumulative or long-term cardiac effects. No funding disclosures were identified in the abstract. The study was observational and self-controlled, so no causal claims about cold-water immersion causing or preventing arrhythmias can be drawn.

About this entry. The Heartwood Review summarizes published, peer-reviewed research in its own words and links to the original source. It is not medical advice; consult a physician before beginning or changing any thermal or recovery practice. Findings summarized here describe the study cited, not any product sold by Teak & Marble Atelier. Corrections.